The present invention relates to a measurement system for measuring average beam power, such as a laser beam, a microwave beam, and the like.
In a laser beam environment having high power laser beam systems utilizing power levels in the range of 100 watts or more, it is desirable to precisely determine the average power of the beam itself.
Some prior art approaches have utilized some form of thermocouple upon which a laser beam is transmitted. The thermocouple provides a signal representative of the magnitude of the power of the laser beam.
Other approaches utilize a calorimeter requiring, in general, some form of flow controller to precisely control the flow of a coolant (typically water) through a heat exchanger. In such prior art approaches, the laser beam is transmitted to the calorimeter, which utilizes some form of thermopile to provide a DC voltage signal corresponding to the power of the laser beam.
U.S. Pat. No. 4,522,511 discloses a continuously flowing calorimeter which uses a thermopile to measure the temperature difference between the inlet coolant and the outlet coolant. The '511 patent also uses a thermopile attached to the inlet and outlet cooling water tubing to eliminate the need for independent temperature sensing devices with possible non-identical characteristics. The method of attaching a thermopile directly to the tubing could lead to errors because of heat loss or heat gain along the tubing, and also as a result of heat flow across the thermopile. The heat absorbed at the absorber may be determined as a function of temperature difference between the coolant in the inlet leg of the conduit and the heated coolant in the outlet leg of the conduit, but does not mention that the temperature difference is also a function of the coolant flow rate.
That patent also requires calibration at a certain coolant flow rate, and the calibration flow rate must be maintained for all subsequent power measurements. This reduces the flexibility in obtaining laser beam power measurements.